So my dad has just acquired a trx with a 900 engine in it. It's actually my old 900 engine that I had in my trx before I fitted the mt09 lump.

He got it in his bike, had it running then the head gasket went. For some reason he put an 850 head on it and it's never run since, and we have bought it back.

So current situation is it cranks over and I can see fuel going in, but it's not trying to start. We have put the 900 rocker cover on with the camshaft position sensor. I'm not sure it's getting a spark. My question is what sensor gives the signal to the ECU to fire the coils, and is it different when its cranking to when it's running normally?

One for the tech boffins!Ps it's running full 900 loom and injectionPps the lad did accidentally fit the battery back to front! I've put a new ECU in to see if that is fired but it's no different

also, using jbx's site to check my sensors - the crank position sensor needs to be 420 to 569 ohms, I tested it and it was 230 ohms. I checked the resistance on my bike, and my father in laws tdm engined trx - all around 230 ohm mark. Dunno whether the values on the site are wrong?

also the camshaft position sensor - says 4.8v on and 0.6v off, Ive tested 3 camshaft position sensors now and they all sit at 4.8v off (not detecting anything) and 0.6v on (detecting the proximity of steel)

I guess the cam sensor is the source of the injector signal...because you only get one cam sensor pulse for every 4-stroke cycle, but 2 crank pulses per 4 stroke cycle. You need the injectors to fire just once per 2 crank rotations (a 4-stroke cycle = 2 crank rotations). Using that signal for fuel pulse would cause extra fuel injection pulses.

The cam sensor is probably working fine if the injectors are firing (assumption)

just checked. so we are getting fuel and we are getting a spark, but the spark seems very weak.

I get surprised by how little a spark is needed, I just sold a little 125 which had a faulty carb originally, but I went down the spark route because it seemed very weak. Once I fixed the carb problem the weak spark was enough for the bike to run normally.

Still worth checking it I suppose, what about the injector wiring ? Presumably the cylinder 1 & 2 injectors are connected to the correct plug and haven't become crossed over in the engine swaps ?

I'll send some pictures across tonight but to get the cam sprockets to line up the crank is at least a tooth past its mark.

Another thing, even when I get the crank lined up I wont be able to get both cams lined up correctly. Timing it on the exhaust cam leaves the inlet cam mark slightly high. but not a tooth high, so if I shuffled it along a tooth it would end up being out the other way. I have had this before on my old TDM850, and it was put down to an element of cam chain stretch.

I'll send some pictures across tonight but to get the cam sprockets to line up the crank is at least a tooth past its mark.

Another thing, even when I get the crank lined up I wont be able to get both cams lined up correctly. Timing it on the exhaust cam leaves the inlet cam mark slightly high. but not a tooth high, so if I shuffled it along a tooth it would end up being out the other way. I have had this before on my old TDM850, and it was put down to an element of cam chain stretch.

pictures will show the full story.

My old (100k mile) 900 cam chain was like that, timing was quite a bit out cams to crank, a couple of degrees. I've had an 850 running even being one tooth out, didn't try the 900 though.....the difference might have been that the 850 was on carbs so no FI timing to consider